Stabilization of 1,1,1-trichloroethane



United States Patent Office 3,454,659 Patented July 8, 1969 ABSTRACT OF THE DISCLOSURE The reaction of 1,1,1-trichloroethane with aluminum is inhibited by the presence in the 1,1,1-trichloroethane of a small amount of a disolved nitrobenzonitrile compound. Concentrations of the order of 0.011 gram mole per liter provide significant inhibition.

Background of the invention This invention relates to the stabilization of chlorinated solvents. More particularly, the present invention concerns the stabilization of 1,1,1-trichloroethane in the presence of metallic aluminum.

Chlorinated hydrocarbons such as trichloroethylene and perchloroethylene are commonly used as solvents in chemical processes, dry cleaning, and metal degreasing. Solvents of this type are subject to slow decomposition and oxidation reactions, particularly in the presence of impurities such as Water, traces of acid or metal salts. Corrosion of metal surfaces in containers and process equiupment and deterioration of solvent quality by formation of acidic and colored byproducts thereby become serious problems. In hibitors such as acid scavengers and antioxidants are commonly added to these solvents in order to prevent such degradative reactions. Inhibitor concentrations are normally of the order of one percent by weight or less.

1,1,1-trichloroethane poses a particularly diflicult stabilization problem because of its unusual reactivity with certain metals, notably aluminum. Traces of metal salts, moisture, or other impurities are not needed to initiate the l,l,1-trichloroethane-aluminum reaction, for this reaction occurs spontaneously on a freshly exposed aluminum surface with spectacular results, converting the solvent and the metal surface in a few minutes to a blackened mass of acidic, carbonaceous material and aluminum salts. Conventional acid acceptor stabilizers cannot be depended upon to inhibit the aluminum 1,1,1-trichlorethane reaction and suitable inhibitors must be discovered by independent investigation. The search has yielded few effective compounds and these show little or no obvious pattern of structure. Typical 1,1,l-trichloroethane formulations contain about five percent by weight of inhibitor which is usually a combination of compounds to inhibit reaction of the solvent with a variety of metals.

Summary of the invention It has now been found that the 1,1,1-trichloroethanealuminum reaction can be substantially retarded or prevented by incorporating into the 1,1,1-trichloroethane an inhibiting amount of a nitrobenzonitrile compound of the formula (CH3)n 2 wherein n is an integer from zero to two. Such compounds may be used alone or in any combination with each other or with other non-reactive conventional inhibitors.

Detailed description Only a quantity of nitrobenzonitrile compound sufficient to retard or to stop the reaction of aluminum and 1,1,1- trichloroethane need be used. Although any significant amount will provide some inhibition, preferably about 0.01-1 gram mole per liter of 1,1,1-trichloroethane is employed and about 0.01-0.1 gram mole is usually most preferred.

Nitrobenzonitrile compounds as defined by the general formula set forth above were tested for inhibiting activity in elongated glass test tubes having an inside diameter of 0.8 cm. and 33 cm. in length. To each vertically disposed tube there was added 0.54 g. of essentially pure 1632 mesh granular aluminum and a solution of the inhibitor in purified 1,1,1-trichloroethane to make a total volume of test mixture of 5 ml. The closed ends of the test tubes were then immersed in an oil bath held at a temperature sufficient to maintain the 1,1,1-trichl0roethane solution in each tube at a steady reflux. The results listed in the following examples indicate the minimum concentration of the inhibitor found effective to provide complete inhibition of the 1,1,l-trichloroethane-aluminum reaction for 24 hours under these conditions. Prevention of the reaction for this length of time under the described conditions indicates capacity for effective inhibition for an indefinite period. Concentrations are given in gram moles per liter, this figure being convertible to weight percent by the equation (moles/liter) (mol. Wt. of inhibitor) 13.46

wt. percent= For example, a concentration of 0.10 g. mole per liter of an inhibitor of molecular weight 134.6 is equal to 1.0 weight percent of that inhibitor.

Effective concentration,

Example gram mole per N0. Compound name liter 1 p-Nitrobenz onitrile O. 03 2 o-Nitrobenzonitrile 0. 07

3 t 4 v hibiting amount of at least one nitrobenzonitrile of the 4. The 1,1,1-trichloroe'thane composition of claim 1 formula wherein the nitrobenzonitrile is o-nitrobenzonitrile.

ON References Cited 5 UNITED STATES PATENTS (CHM 2,043,257 6/1936 Missbach 260-6525 LEON ZITVER, Primary Examiner. wherein n 1s an integer from zero to two.

2. The 1,1,1-trichloroethane composition of claim 1 10 MATTHEW JACOB, Assistant Exammerwherein the nitrobenzonitrile is present in a concentration of 0101-1 gram mole per liter.

3. The 1,1,1-rtrichloroethane composition of claim 1 252-171 wherein the nitrobenzonitrile is p-nitrobenzonitrile. 

